25fi PROCEEDINGS OF THE ACADEMY OF [1885. 



the larger tubercle in Granatocrinus, and the central one, if it 

 exists :it all, the central piece; but whether this plate is exposed 

 or not, we believe it was represented in the Crinoid, and if it was 

 not inserted between the interradials, it was subtegminal, under- 

 neath them. 



In the later stages of Allagecrinns, according to Carpenter 

 and Etheridge (p. 285), the so-called "orals" are plaeed "at the 

 centre of the dome, in close contact laterally, so that no opening- 

 is visible, but their basal angles are more or less truncated, 

 leaving a superficial gap between every pair of plates, which 

 corresponds in position with the articular facet on the subjacent 

 radial." " The interior of this gap, however, is filled up by the 

 deeper portion of the oral plates." This structure, we admit, 

 indicates that possibly at a more advanced stage of the Crinoid, 

 the plates had separated laterally, similar to the orals in the 

 recent Holopus. This, however, which we believe was really the 

 case in Coccocrinus, dbes not prove that the plates of the two 

 groups are homologous, as similar modifications take place among 

 the interradials in the Pahcocrinoidea, or as we should say, take 

 place in the earlier Crinoids exclusively in the interradials, while 

 the tentacular vestibule remains perfectly closed. In the case of 

 Allagecrinus, the opening out of the plates toward the arm bases, 

 indicates, in our opinion, that the Crinoid is approaching the 

 stage of a Platycrinoid, in which the covering plates part the 

 interradials and enter the vault; previous to the later Cyatho- 

 crinoid stage, in which the whole ambulacral skeleton covers the 

 interradials. Coccocrinus represents a transition form between 

 the two former, the interradials being separated from one another, 

 forming open clefts with the ambulacra at their bottom. 



The ventral side of Coccocrinus rosaceus in the best-preserved 

 specimens consists of ten plates, all strictly intcrradial in posi- 

 tion, arranged in live series, which are not in contact laterally 

 nor centrally, leaving live rather conspicuous clefts and a central 

 opening. The outer plate of each series is smaller, the inner 

 resting upon the truncate face of the other. The inner plate at 

 the azygous side is larger, and the anal opening excavated along 

 the suture between the two plates, extending as deeply into the 

 inner as into the outer plate. There are no special anal piece-, 

 neither dorsally nor Neutrally. 



There is no difference of opinion as to the outer plates, whi< h 



